Modern wind turbines are commonly used to supply electricity into the electrical grid. Wind turbines generally comprise a rotor mounted on top of a wind turbine tower, the rotor having a rotor hub and a plurality of blades. The rotor is set into rotation under the influence of the wind on the blades. The operation of the generator produces the electricity to be supplied into the electrical grid.
When maintenance works are required inside wind turbines, hoists are often used in the form of elevator-like structures where a lift platform or a cabin for the transportation of people and/or equipment is hoisted up and/or down within the wind turbine tower. Wind turbines are often provided with working platforms arranged at various heights along the height of the tower with the purpose of allowing workers to leave the cabin and inspect or repair equipment where intended.
Elevator systems, in general, include an elevator car being suspended within a hoistway or elevator shaft by wire ropes. The term wire rope is herein used to denote a relatively thick cable. But in the art, the terms cables and wire ropes are often used interchangeably. In some systems, e.g. for some electric elevators, a counterweight may be provided depending on e.g. the available space. Other systems such as hydraulic elevators normally do not comprise a counterweight.
The service elevators may incorporate some form of traction device mounted on or attached to the elevator. The traction device may comprise a housing including a traction mechanism, e.g. a motor driven traction sheave. The motor typically may be an electrical motor, although in principle other motors could be used.
Service elevators further may incorporate an electromagnetic brake. In addition to this brake, a “secondary safety device” or “fall arrest device” may be mounted on or attached to the elevator. Such a fall arrest device serves as a back-up for the main electromagnetic brake and may typically incorporate some form of sensing mechanism sensing the elevator's speed. The secondary safety device may automatically block the elevator and inhibit any further movement if the elevator moves too fast, i.e. when the elevator might be falling. The speed detection mechanism in this sense acts as an overspeed detector.
A hoisting wire rope of the service elevator or a dedicated safety wire rope may pass through an entry hole in the safety device, through the interior of the safety device and exit the safety device through an exit hole at an opposite end. Some form of clamping mechanism for clamping the hoisting wire rope or the safety wire rope when an unsafe condition exists (i.e. when the overspeed detector trips) may be incorporated in the safety device.
Fall-arrest devices, when fitted to an appropriate wire rope, can be of the type that comprises internal rollers and a clamping mechanism (e.g. involving clamping jaws) which closes onto the safety wire rope, which could be the main hoisting wire rope or a separate safety wire rope. These devices may comprise a centrifugal overspeed detector.
Such an overspeed detector may comprise a driven roller coupled with movable parts that are forced outwardly as the roller rotates when it is driven by the wire rope passing along it. A pressure roller ensures the contact between the wire rope and the driven roller of the centrifugal overspeed detector. If the wire rope passes through the safety device too rapidly, the brake trips and the jaws clamp onto the wire, thus blocking the safety device on the wire rope.
The overspeed detector is provided on the inside of the casing of the fall arrest device. During use of such a fall arrest device, the driven roller may loose contact with the wire rope due to wear. If the contact with the wire rope is lost, then the driven roller does not rotate with a movement of the wire rope (or does not rotate sufficiently rapidly). As a result, an overspeed may not be reliably detected. It is thus important to check whether the overspeed detector is working properly. A little inspection window is generally provided on a sidewall of the casing which allows personnel to check whether the centrifugal overspeed detector is rotating. However, the inspection window does not always allow good visibility of the overspeed detector. Moreover, as the fall arrest device is mounted to the elevator, the inspection window is not always readily accessible for personnel.
Furthermore, even if the overspeed detector can be seen properly and appears to be working well, it is possible that in fact the roller of the detector is not rotating as quickly as it should. Wear to the driven roller (and or pressure roller) can lead to a situation wherein there is still contact between the wire rope and the driven roller, but this contact is not as it should be. As a result, the overspeed detector rotates but is also not capable of reliably indicating an overspeed situation.
The present disclosure provides examples of systems and methods that at least partially resolve some of the aforementioned disadvantages.
Service elevators and related safety devices such as fall arrest devices are not only used in wind turbine towers, but instead may be found in many different sites and structures.
The words “elevators” and “lifts” are used interchangeably throughout the present disclosure.